(1) Field of the Invention
The present invention relates to an ink jet recording medium on which visible images are recorded with an aqueous ink. More particularly, the present invention relates to an ink jet recording medium having excellent ink absorption and image reproducibility and a satisfactory surface strength for office recording sheets and capable of being hand-written thereon by a pencil and allowing pencil marks thereon to be erased with a rubber eraser.
(2) Description of the Related Art
An ink jet recording system using an aqueous ink is advantageous in that noise during the recording procedure is low, colored images can be easily recorded, and the recording procedure can be carried out at a high speed. Thus the application of the ink jet recording system to terminal printer, facsimile machine, plotter and printer for accounting books and slips is progressing. Since usual wood free paper sheets and coated paper sheets usable for conventional printing have an unsatisfactory ink absorption, when these paper sheets are subjected to the ink jet printing, the applied inks are retained in a non-dried condition on the sheet surface for a long time, and thus stain the printing apparatus, the printed sheets and printed images. Therefore, conventional paper sheets are not suitable for the ink jet recording practice.
To solve the above-mentioned problems, Japanese Unexamined Patent Publication No. 52-53012 proposes to use recording paper sheets having a low sizing degree, and Japanese Unexamined Patent Publication No. 53-49113 provides urea-formaldehyde resin-containing paper sheets impregnated with a water-soluble polymeric material.
Also, various types of recording paper sheets having a surface thereof coated with various porous inorganic pigments including amorphous silica which are used for the purpose of enhancing an ink-coloring property and colored-image reproducibility are provided by Japanese Unexamined Patent Publication No. 55-51,583 and No. 56-148,585.
Further, Japanese Unexamined Patent Publication No. 58-110,287, No. 59-185,690, and No. 61-141,584 disclose an improvement in the physical properties of the above-mentioned porous pigments for the purpose of preventing a spread of ink and of forming ink images with high accuracy.
The above-mentioned recording media have a high ink absorption and are capable of recording ink images having a high clarity at a high reproducibility. However, these recording media are still unsatisfactory in surface strength, pencil-writing properties, and erasing properties, of pencil marks, with a rubber eraser, and thus are not suitable as office recording sheets.
To enhance the applicability of the conventional paper sheets to office recording work, for example, pencil writing, employment of a writing-property enhancing agent was proposed by, for example, Japanese Unexamined Patent Publication No. 57-107,878. However, the writing-property enhancing agent does not contribute to enhancing the absorption of water-soluble ink used for printing, and thus when the writing property-enhancing agent is contained in the ink-receiving layer, a problem that the form of printed dots becomes irregular and thus the reproducibility of ink images is decreased, occurs.
Also, Japanese Unexamined Patent Publication No. 4-16,378 proposes to appropriately employ two or more types of porous pigments different in fine pore radius from each other for the purpose of enhancing both the image-reproducibility and the pencil-writing properties. This proposal exhibits a considerable enhancement in both the properties. However, when the amount of coating is increased, to obtain high accuracy images, the pencil writing property is degraded. Therefore the proposal is not satisfactory.
As mentioned above, although an employment of the pigments having a large particle size is proposed for the purpose of enhancing the pencil writing property, since the pigment is not always selected under consideration of ink-receiving property thereof, the reproducibility of high accuracy images is unsatisfactory.